Method of processing substrates using pressurized mist generation

ABSTRACT

A process tank and method for stripping photoresist from semiconductor wafers. In one aspect, the invention is a method for processing integrated circuits comprising: placing at least one wafer having an edge in a process tank having a lid; closing the lid; filling the process tank with a process liquid to a predetermined level below the edge of the wafer; and applying acoustical energy to the process liquid so as to form a mist of process liquid in the process tank. In another aspect the invention is a process tank having a process chamber comprising: a means to support at least one wafer in the processing chamber; means for filling the chamber with a process liquid; a lid adapted to close the chamber; a liquid level sensor adapted to stop the supply of process liquid to the chamber when the process liquid fills the chamber to a predetermined level below a wafer supported in the processing chamber; and an acoustical energy source adapted to supply acoustical energy to process liquid located in the chamber so as to create a mist of the process liquid in the processing chamber.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] Benefit of Provisional Application No. 60/282,351, filed Apr. 6,2001, is claimed.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to apparatus and processes for themanufacture of, more substrates specifically to those used for strippingand cleaning silicon wafers.

[0003] The importance of clean substrate surfaces in the fabrication ofsemiconductor microelectronic devices has been recognized for aconsiderable period of time. Over time, as VLSI and ULSI silicon circuittechnology has developed, the cleaning processes have gradually becomeparticularly critical step in the fabrication process. It has beenestimated that over 50% of the yield losses sustained in the fabricationprocess are a direct result of workpiece contaminant Trace impurities,such as sodium ions, metals, and particles, are especially detrimentalif present on semiconductor surfaces during high-temperature processingbecause they may spread and diffuse into the semiconductor workpiece andthereby alter the electrical characteristics of the devices formed inthe workpiece. Similar requirements are placed on other such items inthe electronics industry, such as in the manufacture of flat paneldisplays, hard disk media, CD glass, and other such workpieces.

[0004] Cleaning of a semiconductor workpiece, and other electronicworkpieces, occurs at many intermediate stages of the fabricationprocess. Cleaning of the workpiece is often critical after, for example,photoresist stripping and/or ashing. This is particularly true where thestripping and/or ashing process immediately proceeds a thermal process.Complete removal of the ashed photoresist or the photoresist/stripper isnecessary to insure the integrity of subsequent processes.

[0005] The actual stripping of photoresist from the workpiece is yetanother fabrication process that is important to integrated circuityield, and the yield of other workpiece types. It is during thestripping process that a substantial majority of the photoresist isremoved or other wise disengaged from the surface of the semiconductorworkpiece. If the stripping agent is not completely effective,photoresist may remain bonded to the surface. Such bonded photoresistmay be extremely difficult to remove during a subsequent cleaningoperation and thereby impact the ability to further process theworkpiece.

[0006] Various techniques are used for stripping photoresist from asemiconductor workpiece. Mixtures of sulfuric acid and hydrogen peroxideat elevated temperatures are commonly used. However, such mixtures areunsuitable for stripping photoresist from wafers on which metals, suchas aluminum or copper, have been deposited. This is due to the fact thatsuch solutions will attack the metal as well as the photoresist. Solventchemistries are often used after metal layers have been deposited. Ineither case, limited bath life, expensive chemistries, and high wastedisposal costs have made alternative strip chemistries attractive.

[0007] Plasma stripping systems provide such an alternative and havebeen used for stripping both pre-and post metal photoresist layers. Thisstripping technique, however, does not provide an ideal solution due tothe high molecular temperatures generated at the semiconductor workpiecesurface. Additionally, since photoresist is not purely a hydrocarbon(i.e., it generally contains elements other than hydrogen and carbon),residual compounds may be left behind after the plasma strip. Suchresidual compounds must then the removed in a subsequent wet clean.

[0008] Ozone has been in various applications in the semiconductorindustry for a number of years. Often the ozone is dissolved indeionized water to form an effective treatment solution. The attractivefeatures of such a solution include low-cost, repeatable processing,minimal attack on underlying device layers, and the elimination of wastestreams that must be treated before disposal. The main drawback withusing such solutions has been the slow reaction rates that translateinto long process times and flow throughput.

[0009] Photoresist strip using ozone dissolved in water has beensomewhat more successful in achieving viable process rate at acceptableprocess temperatures. However, ozone, like all gases, has a limitedsolubility in aqueous solutions. At temperatures near ambient, ozonesaturation occurs at around 20 ppm. Ozone solubility in water increasesdramatically with decreasing temperature, to a maximum of a little over100 ppm at temperatures approaching 0 degrees Celsius and drops toalmost zero at temperatures approaching 60 degrees Celsius. Whileincreasing ozone concentration increases the kinetic reaction rate, adecrease in temperature simultaneously suppresses that rate.

[0010] A technique for stripping photoresist and/or cleaning asemiconductor workpiece using ozone and deionized water is set forth inU.S. Pat. No. 5,464,480, titled “Process and Apparatus for the Treatmentof Semiconductor Wafers in a Fluid”, issued Nov. 7, 1995. The '480patent purports to set forth a method and apparatus in which lowtemperature deionized water is ozonated by bubbling ozone through thelow-temperature water. The low-temperature, ozonated, deionized water isin the form of a bath. Semiconductor wafers are batch processed byimmersing the wafers in the bath, for example, to clean the wafers,strip photoresist, etc. However, this method of stripping wafers usingozone has slow process rates due to the low temperature of the deionizedwater.

[0011] Because of the desirability of using ozone in strippingapplications, additional prior art methods of using ozonated wafer tostrip wafers have been developed. One method includes placing the waferin an ozone rich atmosphere, heating the surface of the wafer, andspraying cold deionized water on the heated wafer surface. However, aswith previous methods of using ozone to strip photoresist from wafersurfaces, this method still has an undesirably slow process rate. Thisis because not enough ozone is reaching the surface of the wafer toreact with and remove the photoresist. This occurs as a result of thedeionized water not having sufficient levels of ozone dissolved therein.

[0012] Another method that has been developed to strip photoresist fromwafers using ozone is to combine the above spraying method with theconcept of mist generation. In performing this method, the wafers areplaced in a process tank. Ozonated deionized water is then supplied tothe process tank so that it fills a bottom portion of the tank. As such,the wafers are not immersed in the ozonated deionized water at all butsuspended above the liquid surface. A heater is connected to the processtank so as to be capable of transferring heat to the ozonated deionizedwater. As the heater provides sufficient heat to the ozonated deionizedwater, a mist of ozonated deionized water is formed within the processtank. Because the mist consists of very tiny droplets of ozonateddeionized water, and because the volume of the process tank above theliquid is filled with an ozone rich atmosphere, the tiny ozonateddeionized water droplets absorb more ozone per volume before theycontact the wafer surface. As such, when these droplets contact thewafer surfaces, they more efficiently strip the photoresist, resultingin faster processing rates. However, these stripping process rates arestill less than optimal. Additionally, apparatus used to perform thismethod can be expensive due to the costs associated with buying andinstalling a proper heating element. Still another problem with thismethod and process tank is that the wafers are positioned in the tankand subjected to the stripping process while in a horizontal position.This impedes the removal of photoresist and increases process time.

[0013] Finally, many of these prior art tanks and methods of usingozonated wafer to strip photoresist cannot be used to perform additionalwafer processing steps such as cleaning, rinsing, and drying. As such,additional process tanks must be purchased.

[0014] Thus, a need exists for a method and apparatus of strippingphotoresist from semiconductor wafers using ozone that result in fasterprocess rates and cheaper equipment. Additionally, a need exists for anapparatus that can perform photoresist stripping and other necessaryprocessing steps, such as rinsing and/or drying, in the same processtank.

SUMMARY OF THE INVENTION

[0015] These problems and others are solved by the present inventionwhich in one aspect is a method for stripping photoresist fromintegrated circuits comprising: placing at least one wafer having anedge in a process tank having a lid; closing the lid; filling theprocess tank with a process liquid to a predetermined level below theedge of the wafer; and applying acoustical energy to the process liquidso as to form a mist of process liquid in the process tank.

[0016] Preferably, the method further comprises applying acousticalenergy to the wafer. It is preferable that the acoustical energy appliedto the wafer be the same acoustical energy that is applied to theprocess liquid. In this embodiment, the acoustical energy applied to theprocess liquid will pass through the process liquid and across thewafer. This acoustical energy can be created by a megasonic transducerpositioned at the bottom of the process tank.

[0017] In performing the method of the present invention, it is alsopreferable that the wafers be placed into the process tank and supportedtherein in a substantially upright position.

[0018] It is preferable for the stripping method to further comprise thesteps of spraying the wafer with the process liquid and filling theremaining volume of the process tank with a process gas. It ispreferable that the process tank be pressurized when the process gasfills the remaining volume of the process tank. Moreover, it is alsopreferable that the process liquid be a multi-fluid mixture comprising aliquid and a dissolved gas, the dissolved gas being the same as theprocess gas. Preferably, the process liquid is ozonated deionized waterand the process gas is ozone.

[0019] The method of this invention can also comprise steps for rinsingand drying wafers following the stripping steps mentioned above. In therinsing process, it is preferable that the method described above forstripping be immediately followed by the steps of: resuming the supplyof the process liquid to the process tank so as to submerge the wafers,fill the entire process tank and overflow the process tank. After apredetermined time, it is preferable that this rinsing process furthercomprise: discontinuing the supply of process liquid; and discontinuingthe application of acoustical energy to the process liquid and thewafers. Alternatively, this rinsing step can involve injecting chemicalsinto the process tank as the process tank is being entirely filled andoverflowed with the process liquid. In order to dry the wafers, it ispreferable that the rinsing step be followed by a drying methodcomprising: draining the process tank; and blowing hot drying gas on thewafers for a predetermined period of time.

[0020] In another aspect, the invention is a process tank having aprocessing chamber comprising: means to support at least one wafer inthe processing chamber; means for filling the chamber with a processliquid; a lid adapted to close the chamber; a liquid level sensoradapted to stop the supply of process liquid to the chamber when theprocess liquid fills the chamber to a predetermined level below a wafersupported in the processing chamber; and an acoustical energy sourceadapted to supply acoustical energy to process liquid located in thechamber so as to create a mist of the process liquid in the processingchamber.

[0021] Preferably, the acoustical energy source is positioned in thechamber so that upon supplying acoustical energy to the process liquid,the acoustical energy passes through the process liquid and across thewafer's surface. In this embodiment, the source of acoustical energy canbe a megasonic transducer located at the bottom of the processingchamber.

[0022] Also preferably, the process tank comprises means to spray thesurface of the wafer with the process liquid when the wafer is supportedin the processing chamber. It is additionally preferable that the wafersupport means support the wafers in a substantially upright position.

[0023] It is further preferable for the process tank to comprise meansto supply a process gas to the processing chamber, the process gassupply means being located above the predetermined level of the processliquid. In this embodiment, the process gas supply means can comprise aconcentration sensor and a pressure regulator. It is preferable that theprocess gas be under pressure when in the chamber. As such, means todepressurize the chamber can be incorporated into the chamber. In thisembodiment, the means to depressurize the chamber can be a properlycontrolled pressure regulator.

[0024] Preferably, the process tank comprises a re-circulation weir,wherein the re-circulation weir is adapted to re-circulate overflowedprocess liquid back into the processing chamber. Also preferably, theprocess tank comprises means to drain the processing chamber.

[0025] It is also preferable for the means for filling the chamber withprocess liquid to comprise a mixing device and a concentration sensor.Moreover, the process tank can be adapted to perform a variety ofsemiconductor processing steps including stripping, cleaning, drying,chemical etching, and rinsing. Finally, the process tank can comprise atemperature sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a schematic cross sectional view of an embodiment of theprocess tank of the present invention, a megasonic process tank.

[0027]FIG. 2 is a flow diagram of an embodiment of the method of thepresent invention, a method for stripping photoresist from wafers at anincreased process rate and decreased equipment cost.

[0028]FIG. 3 is a specially designed wafer carrier capable of properlysupporting wafers in the megazone process tank in accordance with thepresent invention

DETAILED DESCRIPTION OF THE DRAWINGS

[0029]FIG. 4 is a flow diagram of an embodiment of the method of thepresent invention, stripping photoresist from wafers at an increasedprocess rate and decreased equipment costs. The method of FIG. 2 will bedescribed in detail below with respect to the megazone process tankillustrated in FIG. 1.

[0030]FIG. 1 illustrates an embodiment of the present invention,megazone process tank 30. Megazone process tank 30 comprises processingchamber 31 and lid 32. Tank walls 34 form processing chamber 31. Tankwalls 34 are constructed of PVDF with rounded corners and are a minimumthickness of three-eighths of an inch.

[0031] Processing chamber 31 is adapted to receive and support aplurality of wafers 40 in an upright position above the bottom 33 ofprocessing chamber 31. Wafers 40 can be supported in processing chamber31 by a variety of methods. For example, a structure can be built intoor positioned in processing chamber 31 that engages and supports wafers40 with minimal contact. Alternatively, walls 34 of processing chamber31 can modified so as to engage and suspend a wafer carrier as it islowered into processing chamber. However, it should be noted that theexact means by which walls 34 will support a wafer carrier will varygreatly depending on the dimensions of the wafer carrier being used andthe fluid flow requirements of the processes to be performed in theprocess tank. In the illustrated embodiment, support of wafers 40 isachieved by adapting processing chamber 31 to receive and supportspecially designed wafer carrier 41 (FIG. 3). Wafer carrier 41 isdesigned to carry a plurality of wafers 40 with minimal contact andminimal fluid flow obstruction.

[0032] Referring to FIG. 3, wafer carrier 41 can be supported inprocessing chamber 31 by lowering the wafer carrier into processingchamber 31 until handles 42 contact and engage the top of walls 34. Assuch, the wafers 40 are sufficiently lowered into processing chamber 31,supported uprightly, and positioned above bottom 33. As a result, step200 of FIG. 2 is completed. It should be noted that wafer carrier 41 isthe subject of a pending U.S. Patent Application ______ (applicationnumber not yet assigned).

[0033] Referring back to FIG. 1, once the wafers are placed inprocessing chamber 31, lid 32 is closed, completing step 410 of FIG. 4.Tank lid 32 is designed so that when it is closed, ozone withinprocessing chamber 31 can not escape. However, a tight seal is notrequired. Lid 32 is attached to lid controller 35 which is electricallyconnected to a PC having a properly programmed processor. As such,opening and closing of lid 32 can be automated, the closing and openingtimes are controlled by variables inputted by an operator.

[0034] Megazone tank 30 further comprises process liquid supply line 36.Process liquid supply line 36 is fluidly connected to processing chamber31 on one end and mixing device 37 on the other. As such, a fluidconnection is formed, enabling the desired process liquid to betransported to processing chamber 31 from mixer 37 as needed. Thedirection through the fluid lines of megazone process tank 30 are flowis indicated by the arrows.

[0035] Mixer 37 is also fluidly connected to deionized water supply line38 and chemical supply line 39. Deionized water supply line 38transports deionized water from a DIW reservoir to mixing device 37. Itis possible for the deionized water to be ozonated before enteringmixing device 37 in a variety of ways. First, the DIW reservoir itselfcan contain ozonated deionized water. This can occur if re-circulationline 44 fluidly connects DIW reservoir and re-circulation weir 45. Thiswill be described in detail below. A second way by which the deionizedwater can be ozonated before entering mixing device 37 is by fluidlyconnecting an ozone gas supply line to deionized water supply line 38before mixer 37 and dissolving the ozone gas in the deionized waterstream.

[0036] Chemical supply line 39 is also fluidly connected to mixingdevice 37 and can be used to transport a variety of wafer processingchemicals to mixing device 37. Examples of such chemicals are ammoniumhydroxide, hydrochloric acid, hydrochloric acid, hydrogen peroxide,standard clean 1, and standard clean 2. As such, megazone process tank30 can be used to perform virtually any wafer processing step.

[0037] If it is desired by the operator, chemical supply line 39 anddeionized water supply line 38 can supply their respective fluidssimultaneously. This will be dictated by the manufacturing process stepto be performed. The operator controls the flows by variables inputtinginto a PC interface having a properly programmed processor electricallyconnected to mass flow control systems located on the chemical supplyline 39 and the deionized water supply line 38. These types of controlsand methods of coupling these systems are very well known in the art.

[0038] Mixing device 37 can mix the chemical supplied by chemical supplyline 39 and the ozonated deionized water supplied by line 38 to output amulti-fluid mixture into process liquid supply line 36. Liquid supplyline 36 is equipped with concentration sensor 46. Concentration sensor46 can measure the concentration levels of the fluids that make up themulti-fluid mixture passing through process liquid supply line 46 if amulti-fluid mixture is being used. As used herein, the term “fluid”encompasses both a gas and a liquid. Concentration sensor 46 determinesthe concentration levels of a component fluids of the multi-fluidmixture by measuring the conductivity of the multi-fluid mixture as itpasses through. Such concentration sensors are well known in the art.Concentration sensor 46 can be used to monitor and control the ratio ofdeionized water to chemical if a step is being performed in which achemical is being injected into the deionized water stream.

[0039] Returns now to the discussion regarding stripping photoresistfrom wafers 40 according to the method of the present invention, oncethe wafers 40 are positioned in processing chamber 31 and lid 32 isclosed as described above, deionized water is supplied to processingchamber 31 via process liquid input line 36. As deionized water issupplied to processing chamber 31, the deionized water fills the bottomof chamber 31 until liquid level sensor 48 detects that the deionizedwater has reached a predetermined level. Liquid level sensor 48 can be afloat sensor. The predetermined level should be set so that megasonictransducer 49 is covered with a sufficient volume of deionized waterthat ensures that megasonic transducer 49 can be operated without beingpermanently as a result of damage an acoustic mismatch with the gasphase above the liquid. Exact volume requirements are dictated by theamplitude and frequency of the acoustical energy to be supplied bymegasonic transducer 49 and can be easily determined by those in the artfor any specific application. Additionally, the predetermined level mustbe low enough so that the wafers 40 are not immersed at all in thedeionized water liquid. This can be done by ensuring wafers 40 are at ahigh enough position in chamber 31. Once deionized water has filledprocessing chamber 31 to the predetermined level, liquid level sensor 48sends a signal to a properly programmed processor to stop the deionizedwater supply through line 36. This processor discontinues the deionizedwater (DIW) flow into the tank by communicating with a mass flowcontroller (not shown) located on line 38. As such, step 220 of FIG. 2is completed.

[0040] Once the DIW has reached the predetermined level, megasonictransducer array 49 is activated. The use of megasonic transducers insemiconductor wafer processing is very well known in the art. Megasonictransducer 49 emits acoustical energy into the DIW located at the bottomof the tank. By having megasonic transducer 49 positioned on the bottom33 of processing chamber 31, the emitted acoustical energy passesthrough the DIW and comes into contact with the wafers 40. As thisoccurs, megasonic transducer 49 transmits sufficient energy to the DIWto cause small droplets of DIW to break away from the liquid surface andform a mist in processing chamber 31. Additionally, the acousticalenergy passing through the DIW and contacting the wafers 40, thetransmits additional kinetic energy to the wafers 40. This energy helpsto break bonds that hold the photoresist to the wafer and as suchfacilitates stripping of photoresist on the wafers 40. As such step 240of FIG. 2 is completed. Megasonic transducer 49 is activated for apredetermined period of time which is controlled by megasonic controller50. Megasonic controller 50 can be a properly programmed processor.

[0041] By using megasonic transducer 49 to create the DIW mist insteadof a heater as is used in the prior art, two advantages are achieved.First, the megasonic transudcer 49 applies acoustical energy to thewafers 40 which increases stripping rates. Second, because most processtanks already have transducers installed for use in other process steps,no additional equipment is needed. Thus, the extra expenses associatedwith the heater equipment are eliminated.

[0042] Concurrently with applying the acoustical energy the volume ofchamber 31 not occupied by the DIW liquid is filled with ozone gasthrough process gas inlet line 47. Process gas inlet line 47 comprisespressure regulator 51 and gas concentration sensor 52. Pressureregulator 51 and gas concentration sensor 52 are coupled to a properlyprogrammed processor which allows the operator to control flow rates ofthe ozone into processing chamber 31. The ozone is supplied toprocessing chamber so as to be under increased pressure. Increasedpressure of the ozone helps increase the diffusion amounts and rates ofthe ozone gas into the DIW mist. As such, when this DIW with increasedozone concentration contacts the wafers 40, photoresist at an increasedlevel. As such, step 230 of FIG. 2 is completed. Moreover, process gasline 47 can be used to transport any gas needed to process semiconductorwafers, such as carbon dioxide, ozone, nitrogen, chlorine, ammonia, orfluorine. As such, megazone tank 30 can be used to complete almost anywafer processing step

[0043] Also concurrently with applying the acoustical energy, sprayers53 are activated. Sprayers 53 are fluidly connected to the DIW reservoirthat feeds line 38. Upon being activated, sprayers 53 spray DIW on thewafers 40, completing step 250 of FIG. 2. This spray further increasesthe striping process rate. By having the wafers 40 in a substantiallyupright position, the DIW flows down the wafer surface. As such, kineticenergy of the flowing DIW helps remove the photoresist at an even fasterrate. Additionally, having processing chamber 31 filled with pressurizedozone as described above, increases the concentration levels of ozone inall the DIW that contacts the wafers 40, including the DIW from sprayers53.

[0044] Once the wafers 40 have been properly stripped of photoresist,drain valve 54 can be opened, allowing the DIW and the photoresistparticles at the bottom of chamber 31 to exit the processing areathrough drain line 55. At this point, pressure relief valve 56 can beopened, allowing the pressurized ozone to escape through pressure reliefline 57, returning the pressure in processing chamber 31 back to normal.

[0045] Preferably, drain valve 54 is not opened at this time. InsteadDIW line 38 is activated after stripping is completed. As such, DIW isonce again supplied to processing chamber 31 perform a rinse step.

[0046] Upon completion of stripping, megazone tank 30 can be used torinse, clean, and dry the wafers 40. In rinsing the wafers 40, DIW iscontinuously supplied by line 38 through line 36 into processing chamber31. Ozone is also continuously supplied through line 47, ozonating theDIW water as it fills chamber 31. Eventually, the wafers 40 are fullysubmerged in the ozonated DIW and the ozonated DIW fills processingchamber 31 until it is overflowing into re-circulation weir 45. Thisoccurs for a predetermined period of time until the rinsing iscompleted. It is preferable that megasonic transducer 49 be activatedthe entire time to facilitated rinsing and cleaning of wafers 40.Re-circulation weir 45 captures the overflowing ozonated DIW and funnelsit into re-circulation line 44. Re-circulation line 44 transports theozonated DIW back into the DIW reservoir. As such, when the DIWreservoir is used again to supply sprayers 35 or line 38, the DIW willbe ozonated. This will further increase the ozone concentration levelsand will further increase striping rates as the megasonic system isused.

[0047] Moreover, as the ozonated DIW is supplied to the processingchamber 31 for the rinsing step as described above, chemical line 39 caninject desired amounts of cleaning chemicals into the DIW flow. Theexact amounts and identity of the chemicals will be dictated by theprocess requirements and the wafers 40 being processed.

[0048] Once rinsing/cleaning is completed, processing chamber 31 can beused to dry the wafers. A chamber 31 is first drained at a controlledrate by opening drain valve 54. Hot Nitrogen gas can then pumped intoprocessing chamber 31 via process gas inlet line 47. This willfacilitate drying of wafers 40.

[0049] Finally, it is possible to have a temperature sensor attachedsomewhere in processing chamber 31. By coupling the temperature sensorto a processor, optimal temperature can be maintained to maximizestripping process rates and/or ozone solubility in the DIW. This is doneby coupling the processor to a heating or cooling element properlylocated within the megazone system.

[0050] The foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. As will be understood by thoseskilled in this art, the invention may be embodied in other specificforms without departing from the spirit or essential characteristicsthereof. Accordingly, the disclosure of the present invention isintended to be illustrative, but not limiting, of the scope of theinvention, which is set forth in the following claims. Specifically, themethods and apparatus claimed herein are out limited to the productionof integrated circuits but can be used with respect to any flatsubstrate.

What is claimed is:
 1. A method for processing substrates comprising:placing at least one wafer having an edge in a process tank having alid; closing the lid; filling the process tank with a process liquid toa predetermined level below the edge of the wafer; and applyingacoustical energy to the process liquid so as to form a mist of processliquid in the process tank.
 2. The method of claim 1 comprising applyingacoustical energy to the wafer.
 3. The method of claim 2 wherein theacoustical energy applied to the wafer is the same acoustical energythat is applied to the process liquid.
 4. The method of claim 3 whereinthe acoustical energy applied to the process liquid passes through theprocess liquid and across the wafer.
 5. The method of claim 4 whereinthe acoustical energy is created by a megasonic transducer positioned atthe bottom of the process tank.
 6. The method of claim 1 wherein thewafers are placed into the process tank in a substantially uprightposition.
 7. The method of claim 1 comprising spraying the wafer withthe process liquid.
 8. The method of claim 1 comprising filling theremaining volume of the process tank with a process gas.
 9. The methodof claim 8 wherein the process tank is pressurized.
 10. The method ofclaim 8 wherein the process liquid is a multi-fluid mixture comprising aliquid and a dissolved gas, the dissolved gas being the same as theprocess gas.
 11. The method of claim 10 wherein the process liquid isozonated deionized water and the process gas is ozone.
 12. The method ofclaim 2 comprising: supplying the process liquid to the process tank soas to submerge the wafers, fill the entire process tank, and overflowthe process tank after the method of claim 2 is performed for apredetermined period of time.
 13. The method of claim 12 comprising:discontinuing the supply of process liquid after a predetermined periodof time; and discontinuing the application of acoustical energy to theprocess liquid and the wafers.
 14. The method of claim 12 comprisinginjecting chemicals into the process tank as the process tank is beingentirely filled and overflowed with the process liquid.
 15. The methodof claim 13 comprising: draining the process tank; and blowing hotdrying gas on the wafers for a predetermined period of time.
 16. Amethod for processing substrates comprising: placing at least one waferhaving an edge in a process tank having a lid, the wafer being in asubstantially upright position; filling the process tank with ozonateddeionized water to a predetermined level below the edge of the wafer;closing the lid; filling the remaining volume of the process tank withozone, the ozone being under pressure; applying megasonic energy to theozonated deionized water so as to form a mist of the ozonated deionizedwater in the process tank, the megasonic energy passing through theozonated deionized water and across the wafer; spraying the ozonateddeionized water over the wafer surface; and
 17. A process tank having aprocessing chamber comprising: means to support at least one wafer inthe processing chamber; means for filling the chamber with a processliquid; a lid adapted to close the chamber; a liquid level sensoradapted to stop the supply of process liquid to the chamber when theprocess liquid fills the chamber to a predetermined level below a wafersupported in the processing chamber; and an acoustical energy sourceadapted to supply acoustical energy to process liquid located in thechamber so as to create a mist of the process liquid in the processingchamber.
 18. The process tank of claim 17 wherein the acoustical energysource is positioned in the chamber so that upon supplying acousticalenergy to the process liquid, the acoustical energy passes through theprocess liquid and across the wafer's surface.
 19. The process tank ofclaim 18 wherein the source of acoustical energy is a megasonictransducer located at the bottom of the processing chamber.
 20. Theprocess tank of claim 17 comprising means to spray the surface of thewafer with the process liquid when the wafer is supported in theprocessing chamber.
 21. The process tank of claim 17 wherein the wafersupport means supports the wafers in a substantially upright position.22. The process tank of claim 17 comprising means to supply a processgas to the processing chamber, the process gas supply means beinglocated above the predetermined level.
 23. The process tank of claim 22wherein the process gas supply means comprises a concentration sensorand a pressure regulator.
 24. The process tank of claim 22 wherein theprocess gas is under pressure when in the chamber.
 25. The process tankof claim 24 comprising means to depressurize the chamber.
 26. Theprocess tank of claim 25 wherein the means to depressurize the chamberis a pressure regulator.
 27. The process tank of claim 17 comprising are-circulation weir.
 28. The process tank of claim 27 wherein there-circulation weir is adapted to recirculate overflowed process liquidback into the processing chamber.
 29. The process tank of claim 17comprising means to drain the processing chamber.
 30. The process tankof claim 17 wherein the means for filling the chamber with processliquid comprises a mixing device and a concentration sensor.
 31. Theprocess tank of claim 17, the process tank being adapted to perform avariety of semiconductor processing steps including striping, cleaning,drying, chemical etching, and rinsing
 32. The process tank of claim 17comprising a temperature sensor.